An actor’s showcase. Running time: 101 minutes. Rated R (sex, profanity). At the Lincoln Square, the Cinema 1, the 19th Street East and the Loews Village.

‘WE Don’t Live Here Anymore,” a dark comedy centering on a pair of wife-swapping academics, is basically “Who’s Afraid of Virginia Woolf?” re-imagined as an episode of “Thirtysomething.”

Rarely since that me-decadedefining TV series have we seen a pair of such spectacularly self-absorbed overgrown boys as Jack (Mark Ruffalo) and Hank (Peter Krause of HBO’s “Six Feet Under”), both artfully rumpled 30-ish English professors at an unspecified New England college.

They and their respective wives, Terry (Laura Dern) and Edith (Naomi Watts), both stay-at-home moms, are best of friends and frequently socialize – even though Terry correctly suspects her husband is having an affair with the love-starved Edith.

Hank is a casual philanderer who is so absorbed in abortive attempts at writing that he barely notices his wife or their semi-catatonic young daughter (Jennifer Bishop), except to invite the latter to watch him burn his latest unsold manuscript on a barbecue grill.

Jack, though, is a devoted dad to his kids (Sam Charles and Haili Page) and is wracked with guilt over the affair – even as Edith worries about the impact it will have on her friend Terry.

Meanwhile, Terry, who drinks too much, and Hank have a serious flirtation going on – which Jack skillfully manipulates into a physical relationship between his wife and best friend.

In the most powerful scene, Jack demands Terry give him details of her tryst with Hank – which she does, and then erupts into a spectacular fury when she’s dissatisfied by her unhappy spouse’s passive response.

Director John Curran, an American who has worked for many years in Australia, draws skillfully nuanced performances from the four leads, who have rarely been better.

Unusually for an American movie, Curran skillfully delineates the socio-economic differences between the neat, serene existence of the economically well-off Hank and Edith – and the chaotic, messy home life of the financially hard-pressed Jack and Terry.

But Larry Gross’ extremely faithful adaptation of two stories by the late Andre Dubus (author of “In the Bedroom,” whose son wrote “House of Sand and Fog”) is at heart a rather chilly and clinical portrait of four very selfish people.

Since the swapped couples seem to truly care about each other, you may well leave “We Don’t Live Here Anymore” wondering why they don’t simply all settle down as one great big happy family for the kids’ sake.